Pachyostosis

Pachyostosis is abnormal thickening and increased density of bone. In many aquatic vertebrates, it adds ballast that helps counter buoyancy.

Bone remodeling: The lifelong process by which bone tissue is resorbed and replaced. Changes in the balance of bone formation and resorption can produce pachyostosis.
Secondary aquatic adaptation: The evolutionary return of land-dwelling vertebrate lineages to aquatic life. Pachyostosis is one skeletal response to the demands of aquatic living.
Mosasaur: An extinct group of large marine lizards that lived during the Cretaceous Period. Some mosasaurs show skeletal thickening associated with aquatic buoyancy management.
Pachyosteosclerosis: A combination of bone thickening and increased internal bone density. This compound condition includes both features often associated with pachyostosis.
Osteosclerosis: An increase in bone density caused by greater mineralization or reduced internal spaces. Pachyostosis often occurs alongside this density increase, though the terms describe distinct features.
Marine reptile: A reptile adapted to live partly or entirely in marine environments. Several marine reptile lineages evolved pachyostotic bones as ballast.
Nothosaur: An extinct Triassic marine reptile with a long body and paddle-like limbs. Nothosaurs provide examples of early marine reptiles with dense, thickened bones.
Osteoporosis: A disease in which bone mass and structural strength decline. It involves bone loss, opposite to the thickening characteristic of pachyostosis.
Bone histology: The microscopic structure of bone tissue and its growth patterns. Thin sections reveal how pachyostotic bone differs from ordinary bone.
Sirenians: An order of aquatic mammals comprising manatees and dugongs. Their dense ribs and other bones help offset buoyancy while grazing underwater.

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